Conventionally, various methods have been employed to separate solid particles from a waterbody, which included sedimentation, filtration, centrifugation etc. However, said methods have their own limitations when it comes to handling large volumes while separating the solid particles from a waterbody. Further, coagulants and flocculants have been traditionally used in sedimentation, filtration through granular and fluidized (blanket) media, centrifugation, vacuum and pressure filtration, dissolved air flotation and other phase separation processes to enhance the separation. However, there have been common disadvantages of these coagulants while it is being employed with conventional methods such as sedimentation, filtration, centrifugation etc. The conventional coagulants are characterized by high level of swelling and retention of large volume of fluid and they are not entirely stable and tend to produce hydroxide precipitate which considerably reduces the coagulating properties.
Furthermore, to increase phase separation process efficiency during the process of separation, some flocculants such as activated silicic acid have been added to the coagulants. However, addition of such flocculants to the waterbody comprising solid particles requires slow agitation because the formed large flocks often break into smaller flocks by strong agitation. Further, it has been observed that large amount of flocculants and coagulants are required for effective floc-formation. However, since liquid solution of the polymer flocculant has high viscosity, it is difficult to uniformly diffuse the flocculant into the waterbody by slow agitation. In case of employing slow agitation for the purpose of preventing the flocks from being broken into small flocks, it takes a long time to diffuse the polymer flocculant and it causes irregularity in adhesion of the polymer flocculant on the surface of the solid particles and thus sufficient flocculation function cannot be obtained. As a result, an increase in the amount of the polymer flocculant or coagulant added is required.
However, such high dosages of coagulant and flocculant present two fold problems: i) rise in the cost of chemicals, and ii) high chemical content in downstream processing, which would in turn increase the cost of further separation. Nonetheless, the use of waterbody is unavoidable for certain applications such as commercial cultivation of solid particles including but not limiting to living organisms and non-living matter. Hence, there has been a long felt need to overcome the limitation observed in the separation of solid particles from a waterbody.
Separation of solid particles including but not limiting to living organisms and non-living matter from their environments such as waterbody has been a challenge for a long time. Living organisms that are usually found in waterbody include Phototrophs or Photoautotrophs, which are autotrophic organisms that carry out photon capture to acquire energy. A non-limiting example of such organism is algae, a very large and diverse group of simple organisms, ranging from unicellular to multicellular forms.
Currently, the most economically viable method of cultivating such organisms employs the use of open raceways. However, the areal productivity as well as the concentration of such microorganisms in such raceways is extremely low. Harvesting or separation of such organisms from their growth medium per se is technically possible using physical separation methods such as centrifugation and filtration in a single step. However, a very large volume of dilute micro suspension will have to be handled to separate very small amounts of solid organisms. This makes application of physical separation technologies for harvesting of organisms such as algae economically non-viable and extremely challenging. As a result, presently about 30% of the total production cost is attributed to separation or harvesting. The challenge in such separation/harvesting is thus to develop a method that can significantly reduce the fluid volume to be handled or increase the solid concentration resulting in a slurry that can then be handled viably at the secondary harvesting step. As an answer to the above said limitations in the separation of solid particles including but not limiting to living organisms and non-living matter, the Applicants of the instant invention intend to arrive at a distinct method for separation of solid particles from a waterbody.